Are you able to post videos in Lemmy?
Nope. You can just link to external videos though, I'd suggest Streamable if you need to upload something quick.
Do they have any plans to add support for video content do you know?
Not sure. I think videos would be very expensive on the servers so I wouldn't expect it anytime soon. For now I hope they'd just add better embedding support so you can watch videos without leaving the website.